This invention relates generally to temperature measuring apparatus and more particularly to improvements in portable, battery operated, noncontact temperature measuring devices.
Devices for measuring the temperature of remote bodies by noncontact means are well known. Typically, such devices sense and respond to infrared energy radiating from the body. The intensity of such radiation is indicative of the temperature of the body. The following U.S. Patents disclose exemplary temperature measuring devices:
U.S. Pat. No. 3,430,077: BARGEN PA1 U.S. Pat. No. 3,461,380: McGHEE PA1 U.S. Pat. No. 3,535,523: WUNDERMAN, et al. PA1 U.S. Pat. No. 3,722,283: TREHARNE, et al. PA1 U.S. Pat. No. 3,761,713: MERRILL PA1 U.S. Pat. No. 3,780,585: MILO PA1 U.S. Pat. No. 3,791,217: STOUT, et al. PA1 U.S. Pat. No. 3,855,864: DOUGLAS PA1 U.S. Pat. No. 3,921,453: PLATZER, JR. PA1 U.S. Pat. No. 4,111,717: BAXTER PA1 U.S. Pat. No. 4,133,700: HOLLANDER, et al.
A typical noncontact temperature measuring device includes a radiation detector, e.g. a thermopile, for providing a signal indicative of infrared radiation intensity. The detector signal is typically summed with a signal indicative of ambient temperature, i.e. the temperature at the thermopile cold junction, to develop a composite temperature signal indicative of the temperature of the radiating body. In such a device, in order to achieve accurate and rapid temperature readings, it is normally necessary to either control and stabilize the operating temperature of the detector or provide means for compensating for temperature excursions which may be attributable to ambient temperature variations or locally induced thermal effects.
In a portable, battery operated device, it is not practical to provide an adequate temperature control system because of the relatively large amounts of power required. Thus, it is more typical to provide some type of temperature compensation circuitry, which generally relies upon the use of a temperature sensor, such as a thermistor or solid state transducer to measure the departure of the thermopile cold junction temperature from a reference level. However, because of the relative bulk and thermal mass of such thermistors and transducers, they are generally unable to track the cold junction temperature variations with sufficient speed and precision.